This invention relates to tape driving apparatus, and particularly to motor and capstan drives therefor.
In the magnetic tape art, it is usual to employ a motor driven capstan to drive the tape at constant speed past the record and/or reproduce heads located in the tape path to one side of the capstan. A tachometer may be mounted on the capstan shaft to sense incipient variations in the drive speed and to provide information to the driving electronics to correct them by controlling the motor. To avoid "run out" or once-around peripheral velocity variations such as may be caused by any slight eccentricity in the bearings of the shaft, it is usual to mount the roughly finished shaft in precision bearings and to subsequently grind the shaft end as a capstan while the shaft is mounted in the bearings. Both the precision bearings and the mounting process are expensive, and the capstan cannot be replaced in the field without replacing the entire capstan-bearing and motor assembly. Also, the process is not suitable for mounting the usual glass tachometer disc, and any eccentricity in the tachometer mounting can still produce objectionable tape speed errors.
Another problem relates to the mounting of the printed circuit armature disc in the motor. If the disc flexes or is not accurately mounted in a normal plane to the shaft in the zone of brush contact, then poor contact results, together with audible noise and wear and other problems. It has been known in the art to mount the disc upon a solid backing element in the zone of brush contact, but this is not enough to solve all of the problems.
Accordingly, it is an object of the present invention to provide a tape drive in which inexpensive "non-precision" bearings can be used without grinding the capstan after assembly, and without having eccentricity-caused tape speed variations.
It is another object of the invention to provide a printed circuit motor with improved contact between rotor and brushes.